Method for dewaxing oil



Patented May 25, 1937 PATENT OFFLCE METHOD FOR DEWAXING OIL Ross J.Garofalo, Los Angeles, and Claude E. Swift, Glendale, Calif., assignorsto Union Oil Company of California, Los Angeles, (lalifl, a corporationof California No Drawing.

10 Claims.

The present invention relates to the art of separating wax fromwax-bearing oil, and more particularly the invention pertains to amethod in which certain materials are added to the waxbearing oil tocondition the latter so that the wax may be more readily separated fromthe oil. The invention also relates to a process for the production ofmaterials which when added to a wax-bearing oil condition the latter sothat the wax may be more readily removed therefrom.

Many oils contain relatively large quantities of wax which impart a highpour point to the oil and thereby render these oils unsuitable for useas they are solid and will not fiowat ordinary temperatures. In order torender these oils fluid at ordinary temperatures it is necessary toremove the wax present. This is usually accomplished by adding asuitable diluent to' the wax-bearing oil, chilling the diluted oil toatemperature sufficiently low to precipitate the wax and then separatingthe precipitated wax from the diluted oil by settling, filtering orcentrifuging.

We have discovered that wax may be more readily separated from oil bymixing the waxbearing oil with certain materials which render the waxmore readily separable from the oil. Hereinafter the materials which weemploy to condition the wax present in wax-bearing oils in order thatthe wax may be more readily separated from the oil will be referred toas wax modifiers or wax separation aids.

In carrying out our invention the wax-bearing oil is mixed with a smallamount of the Wax separation aid or wax modifier, produced according toour invention, after which the wax-bearing oil containing the smallquantity of the wax modifier is chilled to precipitate the wax from theoil and the Wax is then separated from the chilled mixture by settling,centrifuging or filtering. In many cases it may be desirable to dilutethe wax-bearing oil with a suitable diluent prior to the chilling stepin order to render the oil fluent at the dewaxing temperature. As

diluents for the wax-bearing oil We may employ liquefied normallygaseous hydrocarbons such as ethane, ethylene, propane, propylene,butane or butylene, or mixtures thereof, light hydrocarbons such aspentane, hexane, heptane, octane, nonane, or hydrocarbon fractions suchas naphtha, gasoline, kerosene or gas oil. We may also employ diluentssuch as acetone, acetone and benzol, ethyl alcohol, propyl alcohol,butyl alcohol, methyl ethyl ketone, diethyl ketone, methylpropyl ketone,ethylpropyl ketone, normally gas Application August 12, 1935, Serial No.35,878

eous and normally liquid ethers, dichlorethylene or trichlorethylene ormixtures of these materials With the aforementioned hydrocarbons.

When the diluent employed is one which is normally gaseous at ordinarytemperature (1. e.

60-80 F.) it may also be employed to produce the necessary degree ofrefrigeration to precipitate the wax from the oil by vaporizing aportion of the liquefied norm-ally gaseous material from the diluted oilunder reduced pressure.

Certain petroleum residues (cracked or uncracked) and particularlycertain asphaltic residues contain bodies or substances which when addedto a wax-bearing oil aid in the separation of the-wax from the oil.Direct addition of the petroleum residue to the wax-bearing oil to aidin the separation of the wax therefrom is undesirable because theseresidues contain appreciable quantities of oil fractions whichcontaminate the final dewaxed product. Furthermore,

these oily fractions have little or no eifect upon the structure of thewax and therefore aid in no substantial manner in the separation of theWax from the wax-bearing oil. These oily fractions are merely diluentsand reduce the potency of the wax separation aids present in theresiduum. The residues oftimes also contain undesirable color bodiessuch as asphalt, bituminous material and coke which discolor the finalproduct.

Attempts have been made to recover the wax separation aids frompetroleum residues by distillation. This method is unsatisfactory,however, because the wax separation aids in these residues boil over awide range and they cannot be concentrated in any one particulardistillate fraction. The light distillate fractions as well as the heavydistillate fractions contain appreciable quantities of the waxseparation aids which are diluted with the distillate oils.

We have discovered a method whereby the wax-separation aids may berecovered from petroleum residues in such form as to be substantiallyfree from both the undesirable oily fractions and color bodies presentin the residuum.

In accordance with the preferred method of the present inventionpetroleum residues are extracted with a solvent which will disolve theundesirable oily fractions present but which does not dissolve anyappreciable quantity of the wax separation aids present in the residue.The solvent solution of oily fractions is then decanted away from theinsoluble residue containing the major quantity of the wax. separationaids and the residue from which the oily fractions have been removed isthen distilled and the Wax separation aids are recovered as a distillatefraction.

As solvents for the oily fractions present in the residue we may employliquefied normally gaseous hydrocarbons such as ethane, propane, butaneor mixtures thereof or unsaturated liquefied normally gaseoushydrocarbons such as ethylene, propylene or butylene, or we may usegasoline, naphtha, alcohol and benzol, alcohol and ether, ether andacetone or benzol and acetone. The preferred solvents are the liquefiednormally gaseous paraffinic hydrocarbons and light petroleum naphtha. Bylight petroleum naphtha we mean a hydrocarbon fraction boiling between100 F. and 400 F.

As a specific example of the preferred method of recovering the waxseparation aids a cracked asphaltic residue is distilled with fire andsteam until a still residue is obtained. having a melting point between200 F. and 400 F. (A. S. T. M- Ball and Ring melting point method). Theresidue is then removed from the still and mixed with 3 to 5 parts ofpetroleum naphtha to one part of the still residue and at a temperatureof about 100125 F. This mixture is allowed to settle into two phases.The upper phase comprises a naphtha solution of the oily fractions andthe lower phase comprises the remaining undissolved residue containingthe major portion of .the wax separation aids and such impurities asasphalt bituminous material, coke or color bodies. The upper phaseconsisting of the naphtha and dissolved oily fractions is decanted awayfrom the insoluble residue and this residue is then distilled,preferably with steam at a temperature sufficiently high to cause thewax separation aids to be vaporized and separated from the undesirableconstituents present in the residue. These vapors are then condensed andthis condensate which is substantially free from undesirable oilyfractions and asphaltic bodies is then employed as a wax separation aidin the separation of wax from oil. The temperature employed during thedistillation will range from 400 F. to 650 F.

It will be understood that we may also employ petroleum residues otherthan those which contain asphalt, and that we may also employ uncrackedpetroleum residues as well as cracked residues for the production of ourwax separation aids by the method described alcove. In addition toemploying petroleum residues as the source of our wax separation aids wemay also employ oxidized petroleum fractions, oxidized petrolatum andparafiin wax, heavy extracts produced from petroleum by means ofselective solvents such as nitrobenzene, aniline, cresol, phenol andsulphur dioxide, resinous materials produced during the conversion ofhydrocarbon fractions by a cracking operation, coal tar pitch, gas tarand lignite. These materials contain appreciable quantities of waxseparation aids and may be treated by the above method for theirrecovery.

In some instances it may be desirable to substitute liquefied normallygaseous hydrocarbons for the naphtha in the preceding example as theextractant for the oily fractions present in the crude stock undergoingtreatment. For example the petroleum residuum may be first extractedwith a liquefied normally gaseous hydrocarbon such as liquid propane inthe proportion of one part of the residuum to 3 to 5 parts of liquidpropane at a temperature of about 60 F. to 7 5 F. and under sufficientpressure to maintain the propane in the liquid state. The propanesolution of oily fractions may then be separated from the portion of thepetroleum residue which is undissolved by the liquid propane and thelatter may then be distilled with fire and steam to separate the waxseparation aids present as distillates from the undesirable constituentspresent in the propane insoluble residue. Liquid propane is capable ofdissolving the oil fractions present in the petroleum residue butpossesses a lower solvent power for the wax separation aids present inthe residue than petroleum naphtha.

In some instances it is desirable to further repress the solvent powerof the oil extractant by performing the extraction of the crude stockcontaining the wax separation aid at a reduced temperature. For examplewhen naphtha or liquefied propane is employed as the solvent for theoily fractions present in the petroleum residues, it may be desirable toperform the extraction at temperatures within the range of 0 F. to -25F. At this lowered temperature the naphtha or liquid propane will stilldissolve the oily fractions present in the residue but will dissolveless of the wax separation aids as they are less soluble in thesesolvents at the lowered temperature. As a further modification thepetroleum residues may be intimately mixed with naphtha at a temperatureof about 100 F. and then the temperature of the mixture may be loweredto about 0 F. to 25 F. and after phase separation between the solventand dissolved fractions and the fractions insoluble in the solvent thesephases may be separated. The undissolved portion of the residue is thendistilled in the manner described above in order to separate the waxseparation aids as distillates from the undesirable portions of solventinsoluble residue.

The wax separation aids produced by the foregoing method are effectiveas aids for separation of wax from oil. For example if 0.1 to 1.0% ofthe distillate produced according to the preceding example is mixed Witha wax-bearing oil the wax present in the wax-bearing oil may be morereadily separated from the oil by such methods as centrifuging, coldsettling or filtration.-

The following is an example of dewaxing a wax-bearing oil with the abovedescribed wax separation aids: A waxy distillate of S. A. E. 30 gradehaving a pour point of F. was mixed with 0.5% of the wax separation aidproduced by naphtha extraction and distillation of a cracked asphalticresidue having a melting point of 325 F. This mixture was then dilutedwith liquid propane in the proportion of one part of the waxy distillateto 5 parts of liquid propane at a temperature of about F. The dilutedwaxy oil containing the wax separation aid was then cooled at the rateof about 1 to 3 F. per minute until a temperature of about 35 F. wasattained. The chilled mass was then filtered and the propane was thenremoved from the filtrate by distillation and the dewaxed filtrate had apour point of -5 F.- (A. S. T. M-D--97-30).

It is therefore an object of the present invention to produce waxseparation aids from petroleum residues and other materials whichcontain wax separation aids, undesirable oily fractions and/orundesirable asphaltic or bituminous materials by first extracting thecrude stock with a solvent for the oily fractions present in the crudestock, separating the solvent and dissolved oily fractions from thatportion of the crude stock which is insoluble in the solvent and thenfractionally distilling that portion of the crude stock which isinsoluble in the solvent and recovering the wax separation aids as adistillate.

It is another object of this invention to mix a wax-bearing oil with asmall quantity of the above wax separation aids, chill the mixture ofwax-bearing oil containing the said wax separation aid to a temperaturesufficiently low to precipitate wax and then remove the precipitated waxfrom the chilled mixture by cold settling, centrifuging or filtering.

It is another object of this invention to extract petroleum residuescontaining wax separation aids, undesirable oily fractions andasphalt-like materials with a solvent for the oily fractions, remove thesolvent and dissolved oily fractions'from the residue which is insolublein the solvent, distill said solvent insoluble residue into a distillateand bottom fraction, mix a small quantity of said. distillate withawax-bearing oil, chill the mixture of Wax-bearing oil and distillate toa temperature sufficiently low to precipitate the wax and remove theprecipitated wax from the chilled mixture by cold settling, filtrationor centrifuging.

It is a further object of this invention to mix a wax-bearing oil withthe above described wax separation aid, commingle the wax-bearing oilcontaining the wax separation aid with a diluent, chill the diluted oilto a temperature sufiiciently low to precipitate the wax and remove theprecipitated wax from the chilled and diluted oil by centrifuging,filtering or cold settling. Furthermore, when liquefied normally gaseoushydrocarbons are employed as diluents for the wax-bearing oil containingthe wax separation aid, it is an object of the present invention toproduce the chilling of the oil by vaporizing a portion of the liquefiednormally gaseous hydrocarbon under reduced pressure from the solution.

Another method of recovering the Wax separation aids present in suchmaterials as petroleum residues, cracked waxes, oxidized parafiln,oxidized petrolatum, extracts obtained by extracting heavy oils withselective solvents (such as cresol, nitrobenzene, aniline or sulphurdioxide) oxidized petroleum fractions, coal tar residuum, gas tarresidues and lignite is as follows: The foregoing materials may becontacted or mixed with an adsorbent clay such as fullers earth,diatomaceous earth, Florida clay or Death Valley clay and these clays orearths will adsorb the wax separation aids present. The clay upon whichthe wax separation aids are adsorbed may be recovered from admixturewith the above materials by settling, filtering or centrifuging and thenadded to a wax bearing oil to condition the oil for the separation ofthe wax therefrom. While these clays or earths are capable of adsorbingthe wax separation aids present in the foregoing materials at ordinarytemperature, in many instances it is found to be desirable to contactthe crude stock containing the wax separation aids with the clay orearth at a temperature of 150 F. to 350 F. and then'recover the clayfrom the mixture by settling, filtering or centrifuging.

agitated for a period of about one hour in a closed vessel and at atemperature of about 325 F. After the contact period the hot mixture wasfiltered and the clay thus obtained was found to be very effective as awax separation aid in the separation of wax from oil. We havealso foundthat clays or earths which are recovered as spent clay during the colortreatment of gasoline or lubricating oil are also suitable as waxseparation aids.

If a small amount of the spent clay is added a to a wax-bearing, oil itaids materially in the separation of the wax from the oil. An example ofa spent clay obtained from the treatment of lubricating oil stock is asfollows: A lubricating oil distillate produced from Santa Fe Springscrude oil having a Saybolt universal viscosity of 600 seconds at 100 F.was contacted with Death Valley clay in the proportion of 100 ml. of thelubricating oil distillates to Death Valley clay at a temperature ofabout 325 F. for a period of about 5 minutes. After the contact periodthe hot mixture of clay and oil was then filtered and the clay recoveredin the filter was found to be effective as a wax separation aid for theseparation of wax from oil.

The clays or earths which are recovered after contact with the variouscrude stocks containing the wax separation aids are usually relativelyfree from oil fractions and therefore the addition of these clays orearths to a wax-bearing oil to aid in the separation of wax therefromdoes not result in the contamination of the waxy oil with undesirableoil fractions. Furthermore, these clays or earths do not materiallyimpart to the wax-bearing oil any appreciable discoloration. If desired,the oil content of these clays or earths upon which the wax separationaids are adsorbed, may be lowered by washing the clays or earths withlight solvents such as naphtha, gasoline, liquefied normally gaseoushydrocarbons or benzol, which will dissolve the oil fractions presentbut will not dissolve the wax separation aids to any appreciable extent.By contacting the clays or earths upon which the wax separation aids areadsorbed with these solvents at ordinary temperature i. e. F. to F. orat a lowered temperature i. e. 0 to 30 F. the oily fractions aredissolved in the solvent and may be separated from the clay or earth bysimple decantation of the solvent and dissolved fractions from the clayor earth or by filtration.

The following is an example of employing these clays or earthsupon whichthe wax separation aids are adsorbed in the separation of wax from awax-bearing oil. A wax-bearing oil having a pour point of about F. (A.S. T. M. D-97-30) was mixed with about 2.0% of a clay which had beencontacted with a Santa Fe Springs asphaltic residuum in the mannerdescribed above. To this mixture was added liquid propane in theproportion of one part of the waxy oil to five parts of liquid propane.The diluted oil was then chilled at the rate of about 1 F. to 3 F.

10 grams of the per minute until a final temperature of about F. wasobtained and the chilled mixture was then passed through a filter. Thepropane was removed by distillation and the dewaxed oil was found tohave a pour point of +10 F.

In addition to the use of the above described materials as waxseparation aids, we have found that the resinous materials recoveredfrom crank case oils or from filters employed in connection withinternal combustion engines to purify the lubricating oil employed inthe crank case, have a beneficial effect in improving the dewaxingcharacteristics of wax-containing oils. These resinous materials may berecovered from crank case oils which have been employed in the internalcombustion engine for a thousand miles or more by mixing the used oilwith a suitable diluent, preferably liquid propane, in a closed vesselin a volumetric ratio of say 4 to 8 volumes of propane to one of theoil. The propane precipitates the resinous materials from the oil. Ifdesired, precipitation may be supplemented or aided by lowering thetemperature of the mixture to approximately F. to 40 F. by vaporizing aportion of the propane under reduced pressure. After allowing theprecipitated material to settle, the supernatant solution is decanted.The precipitated resins may be washed with fresh propane to remove anyoil entrained therein after which they are distilled to vaporizeentrained propane. A small amount of these materials, say 1%., issufiicient to aid in the separation of wax from oils by methodsdescribed hereinabove. It is believed that these materials have beenrendered valuable as wax separation aids because of the oxidationconditions existing in crank cases for long periods of time whilemaintained at elevated temperatures. If desired, the precipitated resinsmay be further oxidized with air, oxygen, ozone or hydrogen peroxide atan elevated temperature prior to their use as wax separation aids.

The wax separation aids may be recovered from filters employed inconnection with internal combustion engines by circulating a suitablesolvent, such as benzol, at an elevated temperature through the filter.The solution of solvent containing the materials removed from the filtermay then be distilled to separate the solvent after which the resinousmaterials may be dissolved in a small quantity of heavy oil. Thissolution may then be mixed with propane to precipitate the resinousmaterials in accordance with the procedure described above forrecovering the resinous materials from used crank case oils.

We have also found that asphalt precipitated from asphalt containingoils by means of propane, are valuable wax separation aids. Theseprecipitated asphalts may also be further oxidized and/ or treated inaccordance with methods described above either before or afteroxidation.

It is to be understood that the above examples are merely illustrativeand are not to be construed as limiting the invention which we claim.

We claim:

1. A method for conditioning a wax-bearing oil preparatory to theseparation of Wax therefrom which comprises mixing said oil with a clayor earth containing wax separation aids which have been separated bymeans of said clay from an oil containing the same.

2. A method as in claim 1 in which the wax separation aid is separatedby means of said clay or earth from a cracked petroleum fraction.

3. A method according to claim 1 in which the material containing thewax separation aid is contacted with clay at an elevated temperature.

4. A method of conditioning a wax-bearing oil preparatory to theseparation of wax therefrom which comprises mixing said oil with asubstantially non-volatile oxidized asphaltic residue.

5. A method for conditioning a wax-bearing oil preparatory to theseparation of wax therefrom which comprises mixing said oil with anasphaltic fraction recovered from a used crank case oil.

6. A method for conditioning a wax-bearing oil preparatory to theseparation of wax therefrom which comprises mixing said oil with anoxidized asphaltic fraction recovered from asphalt containing oils bymeans of a solvent.

7. A method of conditioning a wax-bearing oil preparatory to theseparation of wax therefrom comprising mixing said oil with a waxseparation aid recovered from a petroleum residue by extracting saidpetroleum' residue with naphtha to remove the oily fractions present insaid residue, distilling naphtha extracted residue and recovering saidwax separation aid as a distillate.

8. A method of conditioning a wax-bearing oil preparatory to theseparation of wax therefrom comprising mixing said oil with a waxseparation aid recovered from a cracked petroleum residue by extractingsaid cracked petroleum residue with naphtha to remove the oily fractionspresent in said residue, distilling naphtha extracted residue andrecovering said wax separation aid as a distillate.

9. A method of conditioning a wax-bearing oil preparatory to theseparation of wax therefrom comprising mixing said oil with a waxseparation aid recovered from a cracked asphaltic petroleum residue byextracting said cracked asphaltic petroleum residue with naphtha toremove the oily fractions present in said residue, distilling naphthaextracted residue and recovering said wax separation aid as adistillate.

10. A method for conditioning a wax-bearing oil preparatory to theseparation of wax therefrom comprising mixing said oil with a waxseparation aid recovered from a petroleum residue having a melting pointbetween 200 F. and 400 F. by extracting said residue with naphtha toremove the oily fractions present in said residue and said oil freeresidue is subjected to distillation to recover the wax separation aidas a distillate.

ROSS J. GAROF'ALO. CLAUDE E. SWIFT.

Cir

